XANTHIDIUM. 101 



X. FASCICULATUM, (Ehrb.), Ralfs. Plate XXV, figs. 4, 5. 



Semi-cells with four, rarely six pairs of long, subulate, 

 marginal, spreading spines; central projection, minute coni- 

 cal, not beaded. 

 Diameter 55-65 //. without the spines. 



Var. HEXAGONUM, Wolle. Plate XXVI, fig. 5. 



Large angular, with four pairs of short subulate spines. 



Var. MINUS, Wolle. Smaller in size, and spines short. 



Plate XXV, figs. 6, 7, front and lateral view of a semi-cell 

 which appears to develop a sporangium without copulation. 

 I found but one specimen of the kind, and record it as a 

 peculiar abnormal act. 



Var. SUBALPINUM, Wolle. Plate XLV, fig. 9. 



Prof. Delponte, in his DESMIDIACEARUM SUBALPINARUM, 

 p. 168, describes this species differently from that described 

 above, the variation being mainly in the wider separation 

 of the lateral spines. To distinguish the two I make the 

 above variety. 



Not rare in ponds, New Jersey and Minnesota. 



X. ANTILOP^UM, (Breb.). Kg. Plate XXVI, figs. 1, 2. 



Differs from the preceding in smaller size than the typical 

 X. fasciculatum, and in the reverse curvature of the lateral 

 spines. 



Diameter 45-50 /<. 



Var. POLYMAZUM, Nord. Plate XXVI, figs. 3, 4. 



Unlike the true form in the series of bead-like granules 

 over the central protuberance. 



Var. TRIQUETRUM, Lurid. Plate XXV, figs. 1, 2, 3. 



Instead of an oval, end view, this is triangular, similar to 

 a form discovered by the author (Lund.) in Sweden, and to 

 another from Brazil, described by Dr. Nordstedt. 



The only locality for this variety, hitherto found, is a trench 

 near Quakertown, Bucks County, Pa. The other forms may 

 be called common. 



Var. MINNEAPOLIENSE, Wolle. Plate LXIII, fig. 16. 



A new form from Minneapolis, Minn., possessing the pe- 

 culiarity of a fifth pair of aculei immediately over the central 

 protuberance and bead-like series of granules. 



Var. TKUNCATUM, Hast. Plate XLII, figs. 3-5. 



Front, lateral and end views. Same as X. Tyleiianum, 



